KAFO Design Considerations

KAFO Design Considerations

A good KAFO compensates for the biomechanical deficits of each patient by providing control at the ankle and the knee. A physical examination is needed to quantitively measure the biomechanical losses of each joint in order to develop a detailed, custom-designed prescription. The orthosis should interfere with the joint motion as little as possible while effectively correcting abnormal ambulation.

When choosing the materials of an orthosis, we need to take into consideration the cost, weight, safety, and functional reliability of the materials. To minimize the weight of the final product, we have several options: thermoplastics are tough and somewhat flexible; carbon fibers are thin, stiff, and lightweight; aluminum alloys are lighter than steel but subject to fatigue failures; titanium alloys provide strength that is similar to steel but is almost as light as aluminum. 

The design of the orthosis should be structurally sound, functionally reliable, and also user-friendly (easy to put on/take off). We've learned from our research that KAFOs with an anterior opening are easier to put on than brim-style KAFOs (both quadrilateral brim-style and M-L brim-style). Also, to making donning easier, the thigh/femoral shell and the calf/tibial shell should be open on the same side (although the KAFO is structurally more stable if they're open on opposite sides). In other words, the two shells should both have posterior openings or both anterior openings. 
(Click here to read more about different KAFO designs)

With regard to the metal bars connecting the thigh and calf shells, a single, lateral bar provides sufficient support for toddlers since they have small body weight and low activity level. 

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